Salmonella typhimurium mutagenicity has been used to examine the metabolic activation of chemical carcinogens by a form of cytochrome P-450 (HCB-448) purified from lives of 3,4,5,-3',4',5' hexachlorobiphenyl-treated rats. This project will identify carcinogens which are substrates for this form of cytochrome P-450, and allow a comparison with other forms purified from rat liver.